This invention generally relates to medical devices, and particularly intracorporeal devices for therapeutic or diagnostic uses, such as balloon catheters. In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with fluid one or more times to a predetermined size at relatively high pressures (e.g., greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. Stent covers on an inner or an outer surface of the stent have been used in, for example, the treatment of pseudo-aneurysms and perforated arteries, and to prevent prolapse of plaque. Similarly, vascular grafts comprising cylindrical tubes made from tissue or synthetic materials such as DACRON, may be implanted in vessels to strengthen or repair the vessel, or used in an anastomosis procedure to connect vessels segments together.
In the manufacture of catheters, one difficulty has been the bonding of dissimilar materials together. The fusion bonding of a dissimilar material to a substrate material can be extremely difficult if the substrate has a low surface energy. For example, lubricious materials such as HDPE and PTFE, often used to form inner tubular members of catheters to provide good guidewire movement therein, have low surface energies of 31 dynes/cm and 18 dynes/cm, respectively, that make bonding to balloons formed of a dissimilar material such as a polyamide difficult. Prior attempts to address this problem involved providing a multilayered shaft having an outer layer on the shaft configured to be bondable to the balloon. However, a decrease in shaft collapse pressure resistance may result in some cases when the outer layer has a low stiffness. While adhesives may be used in some cases to bond dissimilar materials together, they are not ideal because they can increase stiffness of the component at the bond and some materials do not bond well to adhesives commonly used in medical devices.
A catheter balloon formed of expanded polytetrafluoroethylene (ePTFE) has been suggested. ePTFE is PTFE which has been expanded to form porous ePTFE which typically has a node and fibril microstructure comprising nodes interconnected by fibrils. However, ePTFE has proven difficult to bond to balloon liner materials and/or to catheter shafts. One difficulty has been bonding ePTFE absent the use of adhesives and/or some pretreatment causing decomposition of the fibril structure.
It would be a significant advance to provide a catheter balloon, or other medical device component, with improved performance and bondability.